This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A168595 #7 Aug 15 2017 13:41:41
%S A168595 1,4,36,358,3748,40404,443886,4941654,55555236,629285416,7170731236,
%T A168595 82108083204,943960439086,10889085499348,125974782200478,
%U A168595 1461030555025458,16981658850393252,197757344280343968
%N A168595 a(n) = Sum_{k=0..2n} C(2n,k)*A027907(n,k) where A027907 is the triangle of trinomial coefficients.
%C A168595 Compare to A092765(n) = Sum_{k=0..2n} (-1)^k*C(2n,k)*A027907(n,k), which is the number of paths of length n ending at origin in 1-D random walk with jumps to next-nearest neighbors.
%F A168595 a(n) = 2*A132306(n) for n > 0. - _Mark van Hoeij_, Jul 02 2010
%F A168595 a(n) = Sum_{k=0..n} (-1)^(n-k)*binomial(n,k)*cb(n+k) with cb(n) = binomial(2n,n). - _Peter Luschny_, Aug 15 2017
%p A168595 cb := n -> binomial(2*n, n);
%p A168595 a := n -> add((-1)^(n-k)*binomial(n,k)*cb(n+k), k=0..n);
%p A168595 seq(a(n), n=0..17); # _Peter Luschny_, Aug 15 2017
%o A168595 (PARI) {a(n)=sum(k=0,2*n,binomial(2*n,k)*polcoeff((1+x+x^2)^n,k))}
%Y A168595 Cf. A027907, A092765.
%K A168595 nonn
%O A168595 0,2
%A A168595 _Paul D. Hanna_, Nov 30 2009